Manufacture of internally slitted strips



1962 R. A. WILKINS 3,047,943

MANUFACTURE OF INTERNALLY SLITTED STRIPS Filed July 51, 1958 2 Sheets-Sheet 1 Aug. 7, 1962 A. WILKINS MANUFACTURE OF INTERNALLY SLITTED STRIPS 2 Sheets-Sheet 2 Filed July 51, 1958 BILLET ALTERNATE l PASS ALTERNATE 2 PASS 1 PASS A ALTERNATE 4" PASS 4" PASS e PAssE-TJ TO STRIP MILL M W W m nite States atet 3,547,943 Patented Aug. 7, 1962 flice 3,047,943 MANUFACTURE OF INTERNALLY SLITTED STRIPS Richard A. Wilkins, Rome, N.Y., assignor to Revere Copper and Brass Incorporated, Rome, N.Y., a corporation of Maryland Filed July 31, 1958, Ser. No. 752,223 4 Claims. (Cl. 29-528) My invention relates to the manufacture of tubular bodies such as fluid conducting pipes and tubes, can bodies, and the like, and more particularly to the making of an internally slitted strip the slit of which may be expanded mechanically by introduction thereinto of pressure fluid to convert the strip into such tubular body.

In applicants pending application Serial Number 518,- 768, filed June 29, 1955, is described a method of making metal sheet having between its opposite edges a row of spaced flat slits positioned in its medial widthwise plane. As described by said application, the sheet may be operated upon by a slitter to sever it, along lines positioned between adjacent slits, into a plurality of strips each con taining but one slit. The slit of each strip may be expanded by introduction thereinto of pressure fluid to shape the strip into a tubular body of circular transverse crosssection having at each of its diametrically opposite sides an exterior projecting narrow fin or rib formed by the metal between the edges of the unexpended strip and the adjacent edges of the slit therein.

As further described by said application, the slitted sheet is formed by casting the metal of a billet of oblong transverse cross-section about a row of spaced parallel rods of pulverizable weld preventing material which are of oblong or other flattened transverse cross-section and have their widthwise medial planes positioned in the widthwise medial plane of the billet. The billet is then hot rolled in the direction of the lengths of said rods by passing it between the so-called flat rolls of a mill, with said rods widthwise thereof parallel to the axes of said rolls, for elongating it and reducing its thickness to some where about inch. After such hot rolling of the billet the hot rolled product is cold rolled to elongate it and thin it to the desired gauge, that gauge being twice the desired thickness of the wall of the tubular body to be formed. The sheet so formed is then operated upon by the slitter to form the above mentioned strips, are slits of which strips have their opposite faces substantially in contact and in non-adhering relation.

However, applicant has found that the attempt to produce tubular bodies from the strips severed from sheets made by the above described prior method involves so many difliculties as to make the attempt in many instances commercially unsuccessful especially when the ribs at diametrically opposite sides of the tubular member are to be very narrow. These difliculties arise because when the billet is cast about the row of rods the shrinkage and warping of the metal in solidifying, which solidification does not occur at a uniform rate, or necessarily to the same extent, throughout all portions of the billet, act to displace the rods and move them out of parallelism with each other and the longitudinal edges of the billet, and further arise because the hot plastic rolling of the billet while it is still relatively thick and the rods become pulverized acts to widen at points along their lengths those passages in the then soft billet which were cored by said rods. The overall result of this is that there is no assurance, despite extreme care in the casting and hot rolling operations, that in the final cold rolled sheet the slits will be of precise uniform width throughout their lengths, that their adjacent edges will be precisely parallel to each other, and that such edges will be uniformly straight and not wavy. The lack of preciseness in these ing in the art.

respects makes it extremely diflicult to sever the sheet, into strips each containing a single slit, along lines that are close enough to the edges of the slits to enable the diametrically opposite fins or webs of the tubular body formed from the strip to be narrow enough to secure satisfactory results, because the attempt to secure such closeness frequently results in cutting into the slits at points along their lengths, or, in the case where the adjacent edges of the slits in the sheet are not precisely parallel, results in the forming of diametrically opposite ribs on the tubular body of undesirable extreme width toward one end of that body of. such narrow width toward its opposite end that the strip toward said opposite end will split at the edge of the slit when it is attempted to expand the strip to form the tubular body.

Another way in which such billet may be produced is described in applicants pending application Serial Number 707,522, filed January 7, 1958, and now abandoned. In this other way the weld preventing material, instead of being in the form of pulverizable rods, is in the form of bodies of powder filling preformed passages in the billet. However, the attempt to produce a tubular body from a strip, having a single slit, severed from a sheet formed by use of such billet will give unsatisfactory results for much the same reason as the attempt to produce it from a like strip severed from the sheet made from a billet having the rods of pulverizable material.

Thus applicant has found that the tubular bodies cannot be satisfactorily commercially produced unless there is employed for the purpose a strip having but one slit, the edges of which slit are substantially straight and substantially exactly parallel to each other and to substantially straight parallel edges of the strip. Further, he has found that, to avoid unsatisfactory waste of material in trimming the edge portions of the strip to bring such edges as close to the edges of the slit as is necessary in producing the tubular bodies, it is desirable to have the edges of the final product resulting from the hot rolling operation as close as possible to the edges of the slit in that product and to have such edges of the product substantially straight and parallel to the edges of the slit therein.

Applicant still further has found it impossible from a commercial standpoint to make the above described tubular body by starting with a billet that contains one longitudinally extending body of weld preventing material and hot rolling the billet by the prior method, that is to say, between plain cylindrical rolls with said body width wise thereof always positioned parallel to the axes of such rolls. Commercial considerations require that the edges of the slit in the cold rolled strip which is to be expanded to form the tubular body be positioned reasonably close to the edges of such strip so as to avoid prohibitive waste of material when trimming the edge portions of the strip down to close to the edges of the slit, thus demanding that in the cast billet the edges of the body of weld preventing material also be reasonably close to the adjacent edge of the billet. Still further, commercial considerations demand that in hot plastically rolling the billet by the prior method each pass effect a large reduction in the thickness of the billet so as to reduce the number of passes to a minimum and also before the billet cools to below its annealing temperature form the product which is afterward cold rolled to produce the strip. Applicant has found that, because of the reduced amount of metal in the plane of the body of weld preventing material of the billet having the single body of weld preventing material when the edges of said body are in any way close to the edges of the billet, the billet will split in the width wise plane of such body when it is attempted to so hot roll it, such splitting being commonly termed alligator- Applicant has found that there is no assurance such splitting will not occur in so rolling the billet if the width of said body is to any extent more than the spacing of its edges from the corresponding edges of the billet.

Applicant however has discovered that the billet having a single body of weld preventing material if it is of rectangular, such as square, transverse cross-section, and relatively thick in the direction of each of the sides of such rectangle, can be successfully reduced without alligatoring by plastically hot holling it through a plurality of reducing passes if in most of such passes, including the initial pass, the relatively thin, transversely oblong body of weld preventing material, whether such material in the billet as cast is in the form of a pulverizable rod or mass of powder, is positioned widthwise thereof normal to the axes of the rolls, and if during such rolling the sides of the billet normal to said axes are so acted upon as in effect at least to urge them very strongly toward each other. The rolling of the billet in this way it has been found also will correct any out-ofparallelism between .the edges of said body and adjacent sides of the billet as cast and maintain parallel the edges of said'body so that the product produced by the hot rolling has the above described preciseness. Furthermore, the edges of the hot rolled product will be precisely stnaight and parallel to each other and the edges of the slit formed in such product. The hot rolled product, which is relatively thin, may be cold rolled to produce the final internally slitted strip in the way hereinbefore described, such cold rolling not destroying the preciseness of the hot rolled product and, by reason of the reduction effected by each cold rolling pass being small and the annealing between groups of cold rolling passes, not causing the product to split in the plane of the slit being produced.

Further, and importantly, applicant has found that in hot rolling the billet in the above described improved way the width of the slit in the final product, and the spacing of the slit from the edges of the strip, can be accurately controlled because he has found in hot rolling the billet, with the body of weld preventing material Widthwise thereof positioned normal to the axes of the rolls, that the width of said body and the corresponding width of the billet bear a constant arithmetical relation to each other as the cross-sectional area of the billet is progressively reduced by the several reducing passes, that relation being the same as in the billet as cast. For example, if in the billet as cast the width of the body of weld preventing material is 90% of the corresponding dimension of the billet, it will always be 90% of that corresponding dimension as said dimension is reduced. It has been found, however, that after the billet is hot rolled in this way sufliciently to secure such reduction in the metal as will work it to the extent that its cast structure is materially converted to the characteristic structure of rolled metal, that is to say converted to a structure in which the grains are elongated and interlocked, the billet may be turned through 90 and given a hot plastic rolling pass with said body of weld preventing material widthwise thereof positioned parallel to the axes of the rolls, and without splitting the billet, in this way to, aid in maintaining the rectangular shape of the billet as it is being rolled and reduced in cross-sectional area.

The most effective and convenient way that applicant has found of hot plastically rolling the billet in the above described improved way is by passing it successively through mating grooves of grooved rolls such as are commonly employed in rod mills and blooming mills, as will hereinafter be more fully explained.

In the drawings:

FIG. 1 is an end view of a strip which may be produced from a billet by the improved rolling operation hereinbefore described;

FIG. 2 is an end view of the tubular body which may be formed from the strip according to FIG. 1;

FIG. 3 is a transverse cross-section, on a reduced scale,

4 of a billet for use in producing the strip according to FIG. 1;

FIG. 4 is a fragmentary and more or less diagrammatic side elevation of a 3-high stand of grooved rolls for reducing the billet according to FIG. 3, FIG. 4 showing the position of the billet in its successive passes through the pairs of mating grooves; and

.FIG. 5 is a flow diagram indicating several ways of reducing the billet according to FIG. 3.

Referring to the drawings, the tubular body 1 may be produced by expanding the slit 3 of the cold rolled strip 5 by introduction into such slit of pressure fluid or by opening an end of such slit and then forcing through the slit a cylindrical plug or the like. When the tubular body is thus formed there will be positioned at each of diametrically opposite sides thereof a Web or fin 7 as a result of the edges of the slit being spaced from the edges of the strip.

The strip according to FIG. 1 may be produced from the billet 8 containing the body 9 of weld preventing terial, each of the transverse cross-sectional shape indicated by FIG. 3. By plastically hot rolling the billet to reduce it and said body to give them the cross-sectional shape shown at 10 (FIG. 4) the product of cross-section shown at 10 may be cold rolled in the above described way to produce the strip according to FIG. 1.

As illustrated in FIG. 4, the passes, formed by the mating grooves 11, 12, 13, 14, 15, 16 of the middle grooved roll 17, upper grooved roll 19, and lower grooved roll 21, are of progressively reduced cross-sectional area so that the billet may be progrmsively reduced in cross-sectional area in six successive 'hot plastic rolling passes. In the first, third, fourth and fifth of these passes the body of weld preventing material widthwise thereof is shown as positioned normal to the axes of the rolls, and in the second and sixth passes is shown as positioned parallel to such axes. In the first pass the bottoms of the grooves are shown as so shaped that the billet at its center portion and the width of the body of weld preventing material are more drastically reduced than toward the edge portions of the billet, the pass so shaped permitting this more drastic reduction without allowing the billet unduly to widen horizontally as viewed in FIG. 4, in that way to insure thatthe pass is filled with the metal as the billet is being reduced in cross-sectional area and thus act in effect to cause the opposite side walls of the grooves to press toward each other the metal at each of opposite sides of the faces of the body of weld preventing material. In the second pass the body of weld preventing material is shown as positioned Widthwise thereof parallel to the axes of the rolls. This pass reduces the billet both horizontally and vertically, as viewed in FIG. 4, and removes the bulges positioned toward the opposite sides of the billet coming from the first pass so as again to have a billet of approximately rectangular cross-section, which it has been found facilitates reduction of the billet to the shape shown in the pass formed by the mating grooves 16. In the last pass the billet is shown as so positioned as to cause the body of weld preventing material widthwise thereof to be parallel to the axes of the rolls so as to reduce its thickness by hot plastic rolling to a value best suited to the subsequent cold rolling operation to be performed thereon.

It will be observed that in all of the passes shown by FIG. 4, except the first, the bottoms ofthe grooves are flat except at the corners of the grooves where said bottoms merge into the slightly outwardly tapering sides of the grooves. This tapering of the sides of the grooves facilitates the work entering the passes and discharging therefrom without binding in the grooves.

It will be understood in connection with FIG. 4 that the three rolls are geared together in the usual Way so that the upper and lower rolls rotate in the opposite direction from the middle roll, which permits the work to be passed between the middle roll and lower roll in one direction and, immediately upon its being discharged from between those rolls, to be passed in the opposite direction between the middle roll and upper roll. It will also be understood in connection with FIG. 4 that, although that figure shows the same billet in each of the successive passes, such showing is only diagrammatic and employed for convenience in describing the rolling operation, in which operation of course the billet will be in but one of these passes at a time.

It will be understood that the cross-sectional size of the billet according to FIG. 3 will vary in accordance with the Widths of the strip and slit according to FIG. 1 and also with the amount of strip which it is desired to produce from the billet, in each instance the stand of grooved rolls being so designed as to reduce the billet progressively to the desired size of the final hot rolled product.

The width of the relatively thin, transversely oblong body of weld preventing material, relative to the corresponding dimension of the billet as cast, preferably is as great as conditions will permit. These conditions ordinarily will vary with the metal of the billet and the temperature at which it is hot plastically rolled. With copper, for example, which is hot rolled at an initial temperature of about 1400 F., the width of said body may be as much as 90% of the corresponding dimension of the billet.

The body of Weld preventing material contained in the billet should be of a substance which is stable and cornpatible with the billet at the hot rolling temperature, and if the metal is cast about rods of such substance also stable and compatible with the metal at its pouring temperature. This substance may, for example, be graphite when the billet is of deoxidized copper, but not graphite when the billet is of ordinary oxygen-bearing copper or one of the alloys of iron or nickel that might tend to react with or dissolve graphite; soapstone when the billet is of aluminum, but not soapstone when the billet is of copper or other high melting point metal; and powdered alumina, magnesia, silica or diatomaceous earth when the billet is of oxygen-bearing copper or of steel or other high melting point metal that might react with graphite. In cases where it is desired to employ rods of weld preventing material then powders of the various substances mentioned may be mixed with a binder, such as calcium aluminate, sodium silicate, water-soluble phenolic resins, or the like, and water to form a mixture of requisite consistency to be molded into the form of such rods, and the rods there after dried and baked, if necessary, to cure or fix the binder.

It will also be understood that as the cross-sectional size of the billet according to FIG. 3 is increased more passes may be needed to reduce it by the hot plastic rolling operation to its final desired shape and size. When the billet of increased size cannot be hot plastically rolled in a single 3-high stand of grooved rolls it may be reheated to hot rolling temperature after being operated upon by that stand and further reduced in a second 3-high stand of grooved rolls, and if such reduction cannot be completed in the second stand the operation of reheating the billet and passing it through the grooves of a further stand or stands may be repeated.

The billet need not be reduced in exactly the same way as in the example of such rolling indicated in FIG. 4. For example, in the flow diagram according to FIG. the billet 8 is reduced, in the passes marked 1st Pass, 2nd Pass, 3rd Pass, 4th Pass, 5th Pass and 6th Pass, in the same way as shown in the corresponding passes of FIG. 4. Alternately the billet may, for example, be reduced with the body 9 of Weld preventing material widthwise thereof positioned normal to the axes of the rolls as indicated in the passes marked Alternate 1st Pass and Alternate 2nd Pass, and alternately the billet of the cross-section indicated by the pass marked 3rd Pass may be reduced prior to reducing it to the cross-sectional size and shape indicated by the pass marked 5th Pass to the cross-sectional size and shape indicated by the pass marked Alternate 4th Pass, in which latter pass the body of weld preventing material widthwise thereof is positioned parallel to the axes of the rolls.

The improved method will be further understood from the following example of its practice, to wit:

A 4- x 4 square copper billet 4 feet long is cast about a transversely oblong rod of graphite 3.6" Wide x thick having its edges spaced 0.2" from the adjacent faces of the billet to form a billet according to FIG. 3 and in which the width of the graphite rod is 90% of the corresponding dimension of the billet. This billet is then hot plastically rolled in a 3-high stand of grooved rolls the grooves of which are formed to provide the passes of the shapes shown by FIG. 4. In the first pass, which is formed by the mating grooves 11, the billet will be deformed to one 4 /2" wide and, at its thickest portions, 2 /2 thick, its center portion being 2 thick and the width of the body of weld preventing material still being 90% of such thickness of said center portion or just under 2 inches. The drastic reduction in the crosssectional area of the billet thus effected in the first pass, and particularly at the center portion of the billet where the reduction is greatest, acts to so hot Work the metal as to change its internal structure from that characteristic of cast metal to that characteristic of a rolled or drawn metal, in which rolled metal the grains, as hereinbefore explained, are elongated and interlocked, thus materially increasing the strength of the metal. Because the metal completely fills the pass, and the reducing of its thickness continuously press the edges of the billet under high forces against the side walls of the grooves, the reaction of such side walls against those edges in efiect urges the halves of the billet at opposite sides, respectively, of the vertical medial plane of the billet toward each other under very high forces to prevent splitting of the billet in said plane where the narrow spaces between the edges of the body of weld preventing material and the adjacent faces of the billet present a minimum amount of metal acting to resist such splitting. According to this example, in the second pass,

that is to say the pass formed by the mating grooves 12, the billet has been turned through to place the body of weld preventing material horizontal, that is to say, place it widthwise thereof parallel to the axes of the rolls, the billet being reduced in this pass to one 2%" wide x 2 /2" thick, such positioning of said body being permitted because of the effect produced by the drastic reduction of the center portion of the billet in the first pass. In said second pass the billet is reduced to an approximately rectangular cross-section to eliminate its bulges formed in its upper and lower faces by the first pass and thus facilitate the obtaining of the above men tioned preciseness in the billet in the further steps of reducing it. It has been found that the reduction cannot be further continued after the second pass in this example, with the body of weld preventing material always posi tioned widthwise thereof parallel to the axes of the rolls, without its being almost certain that the billet will split in the medial plane of said body in one of those reductions, and therefore in the third, fourth and fifth passes said body widthwise thereof is positioned normal to the axes of the rolls. In this example the billet in the third pass is reduced to one 2%" Wide x 1%" thick; in the fourth pass to one 1 /8" wide x 1%" thick; and in the fifth pass to one 1%" wide x 1" thick; in all of these passes the body of weld preventing material continuing to be 90% of the thickness of the billet. In the sixth pass, prior to which the metal has been very thoroughly worked, the billet is so positioned that the body of weld preventing material is positioned therein widthwise of said body parallel to the axes of the rolls. In this sixth pass the billet is reduced to a fiat bar 1% Wide x 0.32 thick in which the width of said body is still 90% of the width of the billet, namely, just over 1 /2 inches. During these six passes the thickness of said body will be reduced until in the bar pro- 7 duced by the sixth pass it is about 0.015 thick, that is to say, to form an almost closed slit in the bar.

After the bar produced by the above example of the practice of the improved method has cooled and been pickled and cleaned it is transferred to a strip mill where it is cold rolled, in accordance with ordinary strip mill practice, to reduce it to the desired gauge, which gauge commonly may be anywhere from about 0.020 to about 0.120" depending upon the desired thickness of the wall of the tubular body to be formed. In the strip mill by making the reduction effected by each pass relatively small, and annealing the work when it materially work hardens, the widths of the work and slit therein will not be altered from those of the bar employed as the starting material, the faces of the slit however being brought substantially into contact in the final cold rolled product due to such cold rolling, like the hot rolling, spreading the powdered weld preventing material along the space occupied by it. Such final strip produced by the cold rolling in this example may be expanded to form a conduit, such as shown by FIG. 2, having an internal diameter of approximately 1 inch.

It will be understood, that when it is desired to produce a strip which may be expanded to produce a tubular body of larger internal diameter than that according to the above described specific example of the practice of the improved method, the starting billet must be of proportionately larger cross-sectional area, and the body of weld preventing material therein and the thickness of said body proportionately greater. For example, in a cold rolled strip, which may be expanded to form a tubular body from which may be severed lengths suitable to serve as can bodies 5 inches in diameter, the slit must be about 7 /8 inches wide, and the starting billet must be correspondingly dimensioned to cause to be produced a strip of width requisite to contain a slit of such width.

It also will be understood that within the scope ofthe appended claims wide deviations may be made from the forms of the invention herein described without departing from the spirit of the invention.

I claim:

1., The method of making an elongated internally singly slitted relatively thin and wholly uniform gauge one homogeneous metal strip suitable for use as stock for making a tubular body by expanding the slit, which method comprises forming a cast metal billet containing a singly body extending longitudinally thereof of pulverizable or pulverized weld preventing material stable and compatible with the billet metal at pouring and at hot rolling temperatures, said billet being of substantially rectangular, such as square, transverse cross-section, and relatively thick in the directions of each side of such rectangle, said body of weld preventing material being of relatively thin, substantially oblong, transverse cross-section and positioned substantially coaxially of the billet in direct contact with the metal thereof with its faces and edges parallel to the adjacent faces of the billet, and with the width of such body greater than the distances its edges are spaced from the adjacent faces of the billet with the Width of such body in a high ratio of as much as 90% of the corresponding dimension of the billet; hot plastically rolling said billet to reduce it and said body of weld preventing material to form -a bar of oblong transverse cross-section much narrower and thinner than the original billet, in which bar the thinned body of weld preventing material widthwise thereof is positioned widthwise of the bar with its width relative to that of the bar and the spacing of its edges from those of the bar directly and linearly proportional to the corresponding dimensions of the original billet; such rolling being effected by passing the hot plastic billet successively through a plurality of reducing passes each formed by mating grooves of grooved axially parallel rolls in such wise that in each pass the metal entirely fills it and that at all passes said directly and linearly proportional spacing of the weldpreventing-body edges as in the original billet is maintained, the billet in the first pass and predominantly in the remaining passes being so positioned that the body of weld preventing material widthwise thereof is positioned normal to the axes of the rolls and in the last pass being so positioned that said body widthwise thereof is positioned parallel to such axes; cleaning and pickling the bar so formed by the hot plastic rolling, and afterward thinning it without materially increasing its width by cold rolling it fiatwise to form a relatively thin gauge strip in which the opposite faces of the passage containing the body of weld preventing material of the original billet has been moved substantially into contact to provide said strip with its internal slit and said thin gauge of the strip being uniform throughout and not substantially more than equal to twice the wall thickness for the tubular body to be made by expanding the slit.

2. The method according to claim 1 in which during the hot plastic rolling operation, and after the cross-sectional area of the billet and the Width of the body of weld preventing material have both been materially reduced, the billet is given a reducing pass with said body widthwise thereof positioned parallel to the axes of the grooved rolls.

3. The method according to claim 1 in which during the hot plastic rolling operation, and after the cross-sectional area of the billet and the width of the body of weld preventing material have both been materially reduced, the billet is given one or more times a reducing pass with said body widthwise thereof positionedparallel to the axes of the grooved rolls, each of such passes being immediately preceded and immediately followed by one or more reducing passes with said body widthwise thereof positioned normal to the axes of said rolls.

4. The method according to claim 1 in which the body of weld preventing material is in the form of a pulverizable rod about which the metal of the billet is cast, such rod being crushed by the hot plastic rolling operation to a fine powder which is spread along the passage containing it as the billet is elongated by such rolling and by the coldrolling.

References Cited in the file of this patent UNITED STATES PATENTS 300,730 Pedder June 17, 1884 377,316 Marshall Jan. 31, 1888 377,318 Marshall Jan. 31, 1888 1,331,147 Frauenheim Feb. 17, 1920 2,134,014 Whitehead Oct. 25, 1938 OTHER REFERENCES The Making, Shaping, and Treating of Steel, seventh edition, United States Steel Corp. (page 596 relied on,

v copy in Div, 14), 

